Since commercial deployment of 4G communication systems, to meet the ever increasing demand for wireless data traffic, efforts have been made to develop improved 5G or pre-5G communication systems. As such, 5G or pre-5G communication systems are also called “beyond 4G network” or “post LTE system”.
To achieve higher data rates, 5G communication systems consider utilization of the mmWave band (e.g. 60 GHz band). To decrease path loss and increase the transmission distance in the mmWave band, various technologies including beamforming, massive multiple-input multiple-output (massive MIMO), full dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and large scale antennas are considered for 5G communication systems.
To improve system networks in 5G communication systems, technology development is under way regarding evolved small cells, advanced small cells, cloud radio access networks (cloud RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving networks, cooperative communication, coordinated multi-points (CoMP), reception interference cancellation, and the like.
Advanced coding and modulation (ACM) schemes such as hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC), and advanced access technologies such as filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) are also under development for 5G communication systems.
In general, to provide a wireless communication service to the user, the terminal performs random access to connect to a higher-layer node (e.g. base station). Random access is a procedure for a terminal to connect to a base station to perform wireless communication in a wireless communication system. When initial access or handover is used, the terminal may determine a suitable base station and perform random access with the determined base station. For example, in mobile communication systems such as Wideband Code Division Multiple Access (WCDMA) and LTE of 3GPP, and CDMA2000 of 3GPP2, a random access channel is defined, and random access is performed through the random access channel.
Meanwhile, the Internet is evolving from a human centered network where humans create and consume information into the Internet of Things (IoT) where distributed elements or things process and exchange information. There has also emerged the Internet of Everything (IoE) technology that combines IoT technology with big data processing technology through connection with cloud servers.
To realize IoT services, base technologies such as sensing, wired/wireless communication and network infrastructure, service interfacing and security are needed, and technologies interconnecting things such as sensor networks, machine-to-machine (M2M) or machine type communication (MTC) are under development. In IoT environments, it is possible to provide intelligent Internet technology services, which collect and analyze data created by interconnected things to add new values to human life. Through convergence and combination between existing information technologies and various field technologies, IoT technology may be applied to various areas such as smart homes, smart buildings, smart cities, smart or connected cars, smart grids, health-care, smart consumer electronics, and advanced medical services.
In addition, various attempts are being made to apply high-speed communication technologies to IoT networks. For example, attempts have been made to apply techniques such as beamforming, multiple input multiple output (MIMO), and antenna arrays to IoT networks.
A terminal in an IoT environment often transmits a small amount of data over a long period. For example, an electric meter, which transmits user's power usage through a wireless channel to a higher-layer node (e.g. server), may transmit small data of several bits composed of power usage information and ID information of the meter to the higher-layer node. Such a meter may be more useful in rural areas where the number of users using the communication service is relatively small. Since the area with a small number of users using the communication service has a relatively small infrastructure (e.g. base station), the distance between the infrastructure and the meter may be relatively long.
Even when a small amount of data is to be transmitted, the MTC terminal such as an electric meter must perform random access to the base station to transmit the data. When the distance between the meter and the base station is relatively long, the meter must transmit a random access signal at a high transmission power to transmit a small amount of data to the remote base station. Additionally, when the distance between the meter and the base station is relatively long, the meter may have to repeatedly transmit a random access signal in order to succeed in random access.
Such a random access signal repeatedly transmitted at a high power may cause interference to other terminals and base stations trying to perform random access. In addition, when the distance between the base station and the meter is relatively long, the signal transmitted by the meter or base station may be heavily influenced by the channel condition between the base station and the meter. In the case of a signal for random access, the meter may have to adaptively transmit the signal for random access according to the state of the channel between the base station and the meter.